Preheat oven to 325 degrees. Line 12 muffin cups with paper liners and set aside.
For the crumb topping: whisk together sugars, cinnamon, and salt. Pour the coconut oil over top and using a wooden spoon, mix until incorporated. Then add the flour and mix until combined. Set aside.
For the muffin batter: in the bowl of a stand mixer fitted with the paddle attachment, mix flour, sugar, baking soda, and salt on low speed to combine. With mixer at low speed, add coconut oil one tablespoon at a time; continue beating until mixture resembles moist crumbs, with no visible lumps of coconut oil, 1 to 2 minutes. Stir the egg, egg yolk, vanilla extract and sour cream and mix until all has been incorporated and batter is light and fluffy.
For the cream cheese filling: whip all ingredients together until smooth.
To make the muffins: scoop about 2 tablespoons of muffin batter into each prepared muffin tin. Divide cream cheese filling between each muffin cup and top with more muffin batter. Crumble the topping over each muffin as well. These should look really full!
Bake 20-22 minutes or until toothpick comes out clean once inserted. Dust with powdered sugar. Serve warm or cool to room temperature.